Signaling system



Patented June 26, 1928.

UNITED STATES was i 'AUSTEN M. CURTIS, OF EAST ORANGE, NEW JERSEY, ASSIGNOR TO BELL TELEPHONE LABORATORIES, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

SIGNALING SYSTEM.

Application filed May 3,

This invention relates to signalingsystems and particularly to means responsive to received impulses forcontrolling the operationof a circuit.

In any system of electrical communication it is of great advantage to maintain uniform reception of signals corresponding to a certain normal reception. In practically all systems, however, various influencing factors tend'to cause the signals'to differ from time to time as regards some characteristic, so

that similarly transmitted signals when received under difiering transmission conditions deviate from any normal Which may be established.

In transmitting signals 0X61 long submarine cables, it is always found that an appreciable difference of potential exists between the ends of the cable and that this potential is continually changing, resulting 'in so-called earth currents which may be large in proportion to the strength of the received signal, because of the great attenuation of the signals by transmission over the cable. For this reason it is necessary to prevent these direct currents from reaching the receiving apparatus by making the latter selective against direct or very low frequency alternating currents. The submarine is therefore constructed so that it is incapable of transmitting a direct current from the transmitter through the receiver to ground v This fundamental limitation of the submarine cable transmission system makes it impossible to receive a signal which is a perfect reproduction of the signal impressed on the cable. since it is evident that a signal which consists at the transmitter of a sustained voltage of either polarity will at first, by the transmission ofits higher frequency components. he received at the other end of the cable. but as the transients die out at the transmitter, the received current will also disappear.

When a cable system is handling commercial traltic, it will be found that pecularities of-language and of the telegraph code, or the stopping of certain channels in the 50 operation of multiplex printing .apparatus may cause the positive pulses to preponderategreatly over the negative pulses, or vice versa. during long periods. With the usual type of signal correction a preponderance of cable transmission circuit as used in practice 1926. Serial No. 106,355.

fraction of a second or so, but after that the zero gradually shifts in the-direction of the least frequent signal element.

When the receiving apparatus is the usual siphon recorder, the shifting of the zero, or

as it is commonlycalled, the zero-wander,

caused by the absence of the very low frequencies from the received signals is of relatively minor importance, but when relays are to be operated it becomes essential to limit the zero-wander toa rather small proportion of the total signal. If the shifting of the zero should be more than about.20% of. the normal signal amplitude, the current in the relay windings of the receiving circuit may not be sufiicient to move the armatures of the relays into engagement with both contacts and the relays will fail to opkelrate, thus rendering the signals unintellig1 e.

In the case of printing telegraph systems where the apparatus at the opposite ends of the cable must be held in synchronism the uncertainty of operation of relays caused by zero-wander, in turn causes serious variations in synchronism and may make operation impossible. The principal object of the present invention is to insure reliable and efficient operation of signaling apparatus. For example thejnVention may be employed to compensate 'for zero-wander in the operation of submarine signaling systems.

A further object of the invention is to control a circuit by preventing deviation of impulses from a predetermined normal.

The correction for deviation of signals from normal has been undertaken in various ways. According to one aspect of the present invention a correcting potentialisapplied to signal responsive means Whenever V the zero of the signals has shifted for any tion to insure proper operation of the receiving apparatus, the correcting factor is no longer applied. One feature of the invention relates to a novel type of relay operation whereby certain impulses in one circuit are repro- .duced in a second circuit, whereas certainhaving progressively larger time constants; 'whereby an impulse of very short duration may control a circuit which is responsive only to a sustained impulse.

'. Other-objects and features of the invention will be clearly understood by reference.

to'the accompanying drawing which illustrates a preferred embodiment of the invention as employed in the operation of sub marine signaling apparatus,

In the embodiment of the invention illustrated'a portion of a signal receiving amplifier 10 for submarine signaling is shown in which the last stage of amplification is preferably in the form of a space discharge de vice 11 having a controlelectrode -12. The output circuit of the receiving amplifier comprises the operating winding 13 of a receiving relay 14 or other suitable recording means, such as an ordinary siphon recorder. A preferred arrangement for associating amplifier 10 with a submarine cable is disclosed in my' U. S. Patent No. 1,624,396, April 12, 1927, the last two stages ofthe amplifier therein disclosed being replaced by the two stages of amplifier 10. In circuit with the winding 13 of the receiving relay is the operating winding 15 of a correcti'ng'relay 16 which is preferably a three-position polar relay (similar in construction to that described and shown in my copending application, Serial No. 124,595, filed July 24,

is light and small, and operates between In this type of relay the armature fixed poles of a very strong magnet. The armature is normally held in its mid or neutral position by means of springs 38. The adjustment of the springs is variable to obtain sensitive action of the relay. For the purpose of this invention it is preferable to use contacts made of platinum iridium, one

being fiat and the other sharply pointed. The current through the windings of relay 1 6 is preferably adjusted by means of the contact 24 engaging the series resistance 26 and shunt resistance so that the current in the winding will be that best suited for the purposes of the invention. A similaradjustable series and shunt resistance ar rangement is provided for the relay 14. The

relays or receiving devices. 'For'this reason the various points of the resistances are so chosen, in relation to the resistance of the relay windin that a decrease in'resistance caused b re ucing the size of the shunt on the win 'ng is counteracted by an increase in the series resistance. It may be desirable to have a repeating relay in-series with the recording relay 14 and thelcorrecting relay 16; also an other signal responsive means 1 maybe inc uded in the outputcircuit. The

combination of this-type of relay with its associated circuits is such that a new typeof relay operation is possible,- that is, the relay may beadjusted so that the contact controlled by its armature normally vibrates between the side contacts without touching either;"but, if theamplitude of the deflection of the armature from its said position .shouldmore than a few per cent greater than] normal, momentary contact will be made. It has been found' that a*relay of this type ma be adjusted to operate on a bias of less t an five per centof the signal amplitude. The adjustments of the resistance 18 and of the tap 22 of battery 23' are such that the potential drop through one is just equal and opposite to that of the other and therefore when no signalsvare being received no current flows through the windings 13 and 15 ofthe relays.

Signals received from the cable are suitably amplified and impressed on the receivng circuit including the windings of signal receiving why 14 and correcting relay 16 which controls a compensating circuit for the receiving apparatus. The compensating 1 circuit comprises a storage element such as condenser 17, which as illustrated, may be located in the grid circuit. of the'last stage of the receiving: amplifier and charged by any suitable source of potential through 'suitable resistances as willbe described later.

tery potential, thus preventing the correct-- ing circuit from interfering with the normalamplifier operation. The; adjustment, of the correcting three-position polar relay 16 as outlined above is such that the armature vibrates with the signals between contacts 20 and 21 without touching either, so long'as the zero of the received signal impulses remains substantially constant atits original setting, but if the zero should shift so that the relay armature moves more than a pretie'termined amount further toward one side than toward the other it will engage either contact 20 or 21, completing a circuit through one of the oppositely poled batteries 29 or 30, charging condenser 28. The armature of the relay may damped by any suitable means to render the armature free from. inertia efiects and prevent the ellect of succes:

sive signal impulses from being cumulativeor causing the armature t0 overshoot and make a false contact. This may be efiectively accomplished by electrically damping the relay.

In order that the correction of the signals shall be more eitective the correcting circuit for impressing a compensating potential on the condenser17 has a large time constant and is therefore slow acting, retaining the is immediately charged upon contact of armature 19 with either contact 20 or 21.

The condenser 17 is then charged slowly from condenser '28 through resistances 34 and 35. The charge on these condensers is allowed to leak off through resistance 36. The time constant of the circuit, including condensers 17 and 28 and resistances 34, 35

and 36 depends largely upon the character istics otthe signals being received. but may be of the order of a second. so that the charge on the condenser 17 will be retained an appreciable length of time for correctingpurposes.

In theordinary reception of signals the armature 19 will vibrate with the signals between the'two contacts 20 and 21 without touching either. If. for any reason. the zero of the signals should vary more than a few percent from the original zero setting, toward the negative side for example, the current passing through the windings of the receiving relay 14 and control relay 16 will be of greater amplitude than normally for the negative impulses of the signal and of less amplitude than normally for the positive impulses. The armature 19 of relay 16 will move correspondingly further toward the negative contact than toward the positive, engaging contact 20. Upon the engagement of armature 19 with contact '20. a circuit will be completed so that a positive po-' tential from battery 29 will be impressed directly on the left-hand side of condenser 28. A correspondingnegative potential will be impressed on the right-hand side of the condenser through resistance 31, armature 19, and adjustable resistance 33. In this way the condenser 28 will be charged and its charge will at once commence to flow to condenser 17 through resistances 34 and 35. This charge can leak off through resistance 36. A positive charge on the right-hand side, of condenser 17 will render the potential control electrode 12 less negative and will thereby shift the zero of the signals backtoward the positive side to compensatet'or the original shift of zero toward the negative side. In a similar way, if the zero should shift toward the positive side the armature 19 will engage contact 21 and= 0- tential of the opposite polaritywill be1inpressed on condensers 28 and 17 front battery 30. By impressing negative potential on the right-hand side of eondenser' l'i',

thepotential of the grid 12 ot' the vacuum tube 11 is made more negative, shifting the zero of the signalsitoward the negative side to compensate for wander of the zero toward the positive side of the original adjustment.

The time constant of this circuit being large, the correcting potential will be maintained for a few tenths of a second to compensate for the shift of zero from the original position of adjustment when, it necessary, a further correcting charge will be applied by subsequent contacts of the armature of the correcting relay with either contact point 20 or 21. Since condenser 17 discharges through resistance 36, a prolonged shift of the Zero will cause the armature 19 to make contact again as. soon as the first charge is dissipated sufficiently to permit a reestablishment of a small zero bias. If the zero reverts to its original setting the discharging of condenser 17 will prevent any .ovcr correction. In other words, the correcting action will take place only during periods when such correctlon 1S necessary. If for any reason there should be an over correction or a sudden change in the signal zero tothe opposite side the relay contact would immediately make contact on the opposite side discharging the condenser 28 and charging it oppositely;

' According to the embodiment of the invention described above. when the zero of the signals has shifted beyond a certain maximum amount. the armature 19 in vibrating will engage one of the contacts 20 or 21, impressing a correcting potential on the condenser 28 which in turn will impress a correcting charge on condenser 17 to change the grid potential of discharge device 11 and thereby cause the zero of the signals to shift back'toward the original position. The amounto'f bias or wander of the Zero before applying'a correction can readily be adjusted by changing the position of contacts 20 and 21-01 the relay 16, by adjusting the restoring tension applied to the armature in opposition to the field of the actuating magnets, or by proper adjustment of, the strength of the signal flowing through the windings 15 of the correcting relay 16.

In making the original adjustment of the correcting relay and apparatus and in maintaining the proper operation of the correct- 'ing circuit, a 'novel means is employed for determining the settin of the relay. For this purpose an audi le signal receiving means such as an ordinary loud speaker 40 is inserted in the correcting circuit. The contacts of the correcting relay are then adjusted so that the contact member 19 engages the contacts 20 and 21 with every impulse of an unbiased alternating current used for purposes of testing. With each engagement of the contact making member19 with either contact 20 or 21 a loud click will be heard in the loud speaker. This is due to the alternate charging and discharging of the condenser 28 onthe batteries 29 and 30. The relay operating current is then adjusted by means of the contact 24 and resistances 25 and 26' until the clicks in the loud speaker cease or until they indicate that only one' contact is beingengaged by the armature. This will be evident from 'the fact that the clicks in the loud speaker will be much weaker since the condenser 28 is then not entirely discharging but ismerely receiving "1 small amount of. current from one of the batteries to recharge it to its full capacity. \Vhichever contact is then being engaged is adjusted until no clicks are heard in the loud speaker.

'In the ordinary operation of the correcting circuit when trafiic of ordinarily unbiased nature is being received, there will not'be more than one or two of these clicks in the loud speaker every minute.

It is not necessary that the condenser 17 be Io'ated in the grid circuit of the last stage of the amplifier, as, if proper precautions in circuit design are observed, it may be applied to any other stage of the amplifier or may be associated with any other ele ments of the circuit whereby a compensating influencecan-be impressed on the signals.

As illustrated a filter 37 may be inserted between the condenser 17 and the remainder of, the control circuit-in order to prevent disturbances by. impulses having frequencies higher than the essential signaling frequencies from reaching the condenser. This is particularly desirable when the apparatus is employed in the vicinity of other signal-v ing apparatus which may set up induced currents in any exposed conductors.

It'is', of course, understood that the invention may be employed in connection with 7 other control elements of the circuit or with other signalingsystems than that herein'de scribed without departing from thespirit' and scope of the invention.

\Vhat 1S claimed is: 1. In an electrical circuit. a relay, an armature for said relay movable .with each of a series of variable electricalim'pulses. means for completing a circuit through said armature when and only when said impulses differ from a 'redetermined'normal character, and "means or restoring the normal character of the impulses effective upon said relayas;

a predetermined maximum, and means selecs t-ively actuated in a different sense in accordance with which contact the armature engages.

3..In a signaling system, a relay ha'vi' a movable armature the movement of whic is-' substantially critically damped, which is capable of responding to each of a series of incoming impulses'and circuit control means controlled by said armature, the adjustment of the combination being such that the armaturcgmovesin response to each impulse but withwan amplitude which will not actuate T said'circuit contro means when the impulses are of a-certain character, impulses of a certain different-character causing the armature to actuate said circuit control means selectively inaccordance with the polarity of the impulses.

4. In a zero wander correction circuit, a relayincluding two fixed contacts, an armature contact for said relay movable in response to each of a series of positive and negative impulsesysaid relay being adjusted so that the armature contact will touch a fixed contact when and only when the amplitude of signals of. either polarit-yis increased beyond a predetermined limit, and means to correct zero. wander in accordance with the fixed contact touched by said armature contact. i

5. In a signalingsystem. a relay, an armature. for said relay movable in response to each of a series of variable electrical impulses, means for damping the movement of said armature so asto' eliminate substantially all inertia effects, a contact moved by said armature and stationarycontacts to be pleting a circuit, the adjustment of said com circuit and arelay the armature of which is free from inertia. effect and moves in reengaged by said armature contact for comination being such that said armature contact engages one of said-stationaryacontacts sponse-to each impulse but makes contact.

only in response to impulses of abnormal character, a compensating circuit associated with the receiving circuit and controlled'by said -relay for compensating for the abnormal character of said impulses.

7 Ina signal receiving circuit, the combination of means responsive to each of a series ofs'ignal impulses, means in circuit with 8. In a si nal receivin s'stem a si nal receiving device, a relay controlled by the signals, said relay including an armature in constant vibration, and a correcting circuit comprising circuits having progressively larger time constants, the first of said elements being controlled by said relay and the last of said elements maintaining the zero axis of potential of the received signal impulses operating said signal receivingdevicc substantially the same as that of the impulses transmitted.

9. In a signaling system, an amplifier, a circuit controlled by said amplifier,arelay controlled by said amplifier and adapted to make contact only in response to signals of abnormal character,- a condenserconnected to the input circuit of said'amplifier for controlling the operation thereof, said relay con trolling the charge on said condenser and means associated with said condenser for causing the charge thereon to compensate for the abnormal character of the signals.

10. In a signal receiving system, a receiving circuit, a condenser associated with said receiving circuit, control circuit for said condenser comprising a second condenser, and a relay controlled by the signals and adapted to impress a charge on said second condenser in res onse only to abnormal signals, said secon condenser controlling the charge on said first condenser, and means associated with said first condenser for causing the charge thereon to compensate for the abnormal character of said signals.

11. Terminal apparatus forsubmarine signahng conductors comprising a receiving amplifier, a correcting circuit connected to axis of potential of the transmitted signals. 12. Terminal apparatus for submarine -'signaling cable comprising a receiving circuit, a correcting circuit associated with said receiving circuit, and including a condenser, a relay controlled by the signals and adapted to make contact only in response to abnormal signals, a source of potential connected in circuit with said condenser by the operation of saidrelay to correct for the abnormal character of the signals, and means to shield said condenser from high frequency disturbances in the correcting circuit.

13. In a submarine .cable signal receiving device, a relay controlled by the signals anda corrective circuit for maintaining the zero axis of potential of the received signal 1mpulses operating said signal receiving device substantially the same as that corresponding to the zero axis of potential of the signals transmitted, said corrective circuit comprising a condenser, a resistance element, means comprising a contact moved by the armature of said relay for charging said condenser through said resistance element, a second condenser, a second resistance element and meansfor charging said second condenser through said second resistance element from said first condenser.

14. In a submarine cable signal receiving device, a relay controlled by the signals and a corrective circuit for maintaining the zero axis of potential of the received signal iinsaid first condenser, and a high resistance leak path through which said second con-' denser may discharge.

15. In a submarine -cable signal receiving system, a signal receiving device, a relay controlled by the signals and a corrective circuit controlled by said relay for maintaining the zero axis of potential ofthe received signal impulsessubstantially the same as that corresponding: to the zero axis of potential of the signals transmitted, said 'corcharging circuit therefor. including a contact moved by the armature of said relay, a second condenser and a discharge circuit for said first condenser including said second condenser.

16; A submarine cable signal receiving system, a signal receiving device, a space discharge voltage controlled relay for re-' peating received signals,a condenser, a relay a second resistance element,

Irective circuit comprising a condenser, a

and means for causing the charging and discharging of said condenser to vary the control potential of-said s ace discharge relay.

;17. A submarine ca le signal receiving system, a signal recelvin device, a space discharge, voltage contro ed relay for repeating received signals, a condenser, a relay, having contacts and two oppositely poled sources of potential controlled by said contacts for charging said condenser when and only when signals are received which deviate a certain, amount from those normally' 7 transmitted, and means whereby the charging ofsaid condenser varies the control po.-'

tential of said spacedischarge relay.

18. A submarine cablesignal receiving 8 stem, a signal receivin device, a. space discharge voltage control ed relay for re peatinfi received signals, a condenser, a relay contro ed by space discharge relay for charging said condenser when and. only when'signals are received which deviate in a certain manner and amount from those normally transmitted, a second condenser associated with the input circuit of said space discharge relay and means whereby t e potential of said first condenser controls the operating potential of said space discharge relay.

19. In combination, a signal responsive device, a signaling circuit for impressing signals thereon, a correcting circuit comprising terminals connected to said signaling circult, contacts operated by said device in response to an abnormal signal for applying a correcting voltage to said terminals, and means between said terminals and the source of correcting voltage for smoothing out the abrupt changes in. voltage which might otherwise be caused by operation of said contacts. I I I 20. In an electrical system a series ofcirmam.

. my name this 1 cuits having progressively larger time con- J stants, means responsive to each of a series of impulses, the first of said circuits being duration and the last of said circuits being actuated completely only in response to the accumulative effect of aplurality "of impulses. f

21. In a signaling cir'cuita plurality of relays in circuit, one of which relays is actuated by received signals and another of which is responsive to each signal impulse received, but operated ,only in response to signals of an abnormal" character.

22.- In a si nal receiving circuit a receiving relay and withsaid receiving relay, said receiving relay being and sai only .to impulses of abnormal amplitude.

" 23. In a submarine signalin circuit a a corre'ctingre'lay in circuit signal receiving amplifier, a p urality of signal res nsive devices in the output of saidamplifier, and an adjustable'series and shunt resistance for each o f said signal rep 'sponsive devices for controlllng the propor- 7 tion of the total current received by each device without altering the current through the other devices.

24. A telegraph receiving system compris ing-the usual receiving apparatus and additional means for indicating audibly a de-:-

tional means including atelephone receiver as an indicating element for indicating audibly a departure of the zero axis of received impulses to a predetermined extent from normal conditions.

In witness whereof, I hereunto subscribe day of Ma A. D., 1926. AUSTE M. CURTIS. 

